This invention relates to an anti-intruder security system and more particularly to a system which provides an optical veil in the IR spectral region which sets up an alarm when being, breached
Optical security systems having different configurations for detecting of intrusion into areas protected by light beams are known and operate along borders between countries, in the region of industrial areas and even surround houses.
In general such systems include one or more light sources which illumination is detected by at least one oppositely mounted detector which is located at some distance apart and which activates an alarm when the optical way between the source and the detector becomes blocked.
Both the light sources and the light detectors are usually mounted on posts or towers to form a peripheral or a straight fence, the towers can be equipped with solar cell panels and electrical storage devices to facilitate system operation in remote areas.
Besides, each tower may be connected by a wired or wireless communication network to a control center which allocates the blocked detector, thus estimating the location of the intrusion.
U.S. Pat. No. 6,806,811 to Readler describes an anti-intruder perimeter fence based on IR emitters and detectors (transceivers) arranged in series wherein each transceiver device generates a unique IR signal to distinguish it from another transceiver in the fence.
U.S. Pat. No. 6,965,109 to Iwasawa describes a multistage active infra red sensor in which each detector on a tower is affected only by the illumination of a single emitter in an adjacent tower.
U.S. Pat. No. 6,965,315 to Ikeda describes an anti-thief security sensor assembly in which the angle of an optical unit can be adjusted and U.S. Pat. No. 6,801,128 to Houston describes a tower of an anti-intruder system which may utilize multiple detection beams and which includes a solar cell panel.
Recently, an anti-thief security sensor assembly capable of automatically setting the projecting power from the emitter to the detector was described in U.S. Pat. No. 6,998,982 to Iwasawa.
In most of the mentioned above prior art systems, the configuration and mode of operation is such that the optical pathways which are produced between the light sources and their respective light detectors are parallel to the ground and to each other, i.e. that each light detector is responsive to a beam of illumination which is emitted from a single light source which is mounted oppositely and horizontally to that detector. Such a simple spreading of light beams is shown in FIG. 1.
While this arrangement, in which the light detector becomes completely “darkened” when the appropriate impinging ray of light is being blocked (because rays of light from other sources which were not blocked, do not interfere) has the advantage of a great signal to noise ratio, it has the inherent disadvantage of being inefficient because only a small fraction of the source power (a single beam) is utilized for the assessment of the disturbing event.
Another major problem of the anti-intruder systems described above is a high rate of false alarms, which could have been minimized if the alarm provoking element is identified, e.g. by providing its image.
To overcome this deficiency, a dense optical network, which requires a great number of source/detector pairs, will be needed; this however puts a burden on the cost and on the electrical supply of the system, which impedes its use in a stand-alone mode in remote regions.
Because nowadays systems have a limited number of optical channels which are breached by an intruder they fail to produce a sufficiently detailed image of the intruder and are therefore subjected to a high rate of false alarms.
There is therefore a need in the art for an improved anti-intruder system which will eliminate these mentioned above drawbacks.
The present invention lifts off these drawbacks and provides related advantages